Severe Thunderstorm Warning 82, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-250600-

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
300 PM MST THU AUG 24 2006

SOUTHWEST AND SOUTH-CENTRAL ARIZONA...AND SOUTHEAST CALIFORNIA
FORECAST DISCUSSION

.SYNOPSIS...
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS OVER MUCH OF THE
REGION TONIGHT AS THE AIRMASS REMAINS MOIST AND UNSTABLE. THE CHANCE
FOR THUNDERSTORMS WILL CONTINUE FRIDAY...BEFORE AN APPROACHING LOW
PRESSURE AREA BRINGS DRYING TO SOUTHEAST CALIFORNIA AND SOUTHWEST
ARIZONA. THIS DRIER AIR WILL SPREAD OVER THE ENTIRE REGION BY THE
WEEKEND...CONFINING ANY THUNDERSTORMS TO THE HIGHER TERRAIN OF SOUTH
CENTRAL ARIZONA. A MOIST SOUTHEAST FLOW IS EXPECTED TO RETURN THE
MIDDLE PART OF NEXT WEEK...FOR AN INCREASING CHANCE OF SHOWERS AND
THUNDERSTORMS.

&&

.SHORT TERM...
TONIGHT THROUGH SUNDAY...
ANOTHER VERY ACTIVE MORNING ACROSS SOUTHWEST AND SOUTH-CENTRAL
ARIZONA TODAY. ODD...REALLY...FOR THIS TIME OF YEAR...YET OBVIOUSLY
NOT OUT OF THE QUESTION. SCATTERED SHOWERS AND THUNDERSTORMS BEGAN
AROUND 5AM THIS MORNING AND HAVE BASICALLY CONTINUED ACROSS PORTIONS
OF LA PAZ...YUMA...MARICOPA...AND PINAL COUNTIES THROUGHOUT THE DAY.
THE BIGGEST THREAT WITH THESE STORMS HAS BEEN RAINFALL...WITH
SEVERAL PLACES IN THE VALLEY RECEIVING OVER AN INCH...WITH INDIAN
BEND WASH OVER 2.5 INCHES. SEVERAL URBAN AND SMALL STREAM FLOOD
ADVISORIES HAVE BEEN ISSUED...AND WELL CONTINUE TO MONITOR
FLOODING AS THE AFTERNOON WEARS ON.

MEANWHILE...SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ARE
DEVELOPING OVER SOUTHWEST MARICOPA COUNTY...AS WELL AS LA PAZ AND
YUMA COUNTIES. STORMS ARE MOVING IN A GENERAL NORTHEAST DIRECTION
(AGAIN...ODD FOR THIS TIME OF YEAR)... AT A RATE OF ABOUT 5-10 MPH.
WILL THESE STORMS CONTINUE TO MOVE NORTHEAST INTO THE VALLEY? GOOD
QUESTION. LOOKING AT THE IR SAT IMAGERY...WE SEE CLOUD TOPS
CONTINUING TO COOL AS THEY MOVE IN THE GENERAL DIRECTION OF MARICOPA
COUNTY...INDICATING TALLER STORMS WITH DEEPER CONVECTION. WE DIDNT
HAVE AN AFTERNOON KPSR SOUNDING TODAY...BUT LOOKING AT THE 12Z KPSR
SOUNDING FROM THIS MORNING AND USING A MEAN MIXING RATIO FROM
1000-700MB OF ABOUT 12 G/KG (PRETTY IMPRESSIVE AMOUNT OF MOISTURE)
AND AN AFTERNOON HIGH OF 92 (PERHAPS A BIT OPTIMISTIC GIVEN THE 2:30
PM TEMP OF ONLY 89) WE GET A GOOD AMOUNT OF CAPE (NEAR 1000 J/KG).
HOWEVER...THERE IS AN AREA OF CIN WED HAVE TO OVERCOME IN ORDER TO
GET STORMS GOING ONCE AGAIN IN THE VALLEY...WHICH IS POSSIBLE AS
SURROUNDING AREA STORMS SEND OUTFLOWS THROUGH THE METRO AREA. THAT
SAID...WILL KEEP ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS
FROM THE RIVER EAST THROUGH THE EARLY EVENING HOURS.

SO WHY ARE WE SEEING STORM DEVELOPMENT UNDER A SOUTHWESTERLY
FLOW...WHICH IS NORMALLY A DRY REGIME? EARLIER THIS MORNING WE
NOTICED SOME VERY LOW CLOUDS MOVING NORTHWARD ALONG THE BAJA
PENINSULA AND INTO YUMA COUNTY. KYUX VAD WIND PROFILE AS WELL AS MID
MORNING SOUNDINGS HAD A PRETTY GOOD LOW LEVEL SURGE GOING ON WITH
WINDS OUT OF THE SOUTH AT 15 TO 20 KTS. MEANWHILE...THE TROF OF LOW
PRESSURE OVER THE PAC NW IS RESULTING IN SOUTHWESTERLY WINDS OVER
THE WRN CWA...WHICH HAS PULLED THE MOISTURE COMING UP THE GULF OF CA
INTO THE WESTERN DESERTS. ALSO...TROPICAL STORM ILEANA CONTINUES
DOWN SOUTH...SENDING WAVES OF MOISTURE UP THE GULF AND INTO THE
DESERT SW. ALTHOUGH SHE IS TAKING A MORE WESTERLY TRACK THAN WHAT
WAS EXPECTED YESTERDAY AT THIS TIME...I CANT HELP BUT THINK SHE IS
HELPING TO SUSTAIN THE MOISTURE OVER THE WRN DESERTS...WHICH WOULD
NORMALLY HAVE BEEN WASHED OUT VIA A DRY SOUTHWESTERLY SYNOPTIC FLOW.

THAT ALL SAID...I ADDED SLIGHT CHANCE POPS FOR SE CA...INCREASING AS
YOU GO EASTWARD...FOR TONIGHT AND AGAIN FRIDAY. THE SYNOPTIC FLOW
WILL EVENTUALLY WIN OUT...WITH RATHER RAPID DRYING FROM WEST TO
EAST...BUT THE EARLIER MODEL RUNS MAY HAVE BEEN A BIT HASTY WITH
THIS. LATEST THINKING IS THE DRY AIR WONT USHER INTO OUR WRN
DESERTS AND SOUTH-CENTRAL DESERTS UNTIL SAT/SUN...WHERE THEN THE
CHANCE FOR SHOWERS AND THUNDERSTORMS ARE BASICALLY CONFINED TO THE
HIGHER TERRAIN OF SOUTHERN GILA COUNTY. MEANWHILE...THE NEXT DAY OR
SO COULD BE INTERESTING...AS THE ATM REMAINS MOIST AND WE ARE UNDER
A TRANSITION EVENT AT THE SYNOPTIC SCALE.

&&

.LONG TERM...
PREVIOUS DISCUSSION...
SUNDAY NIGHT THROUGH THURSDAY...
BY SUN UPPER TROF MOVES OVER AZ WITH FAIR AMOUNT OF DRYING ACROSS
THE ENTIRE REGION. AS TROF MOVES TO THE EAST MON...A UPPER HIGH SETS
IN OVER THE GREAT BASIN RESULTING IN DRY NORTHERLY FLOW FOR MUCH OF
THE REGION. THIS LOWERS P-WATER DOWN TO HALF AN INCH. BUT SOME
LIMITED MOISTURE IS EXPECTED TO REMAIN OVER THE HIGHER TERRAIN OF
SOUTH CENTRAL AZ AND WITH AFTERNOON HEATING...A SLIGHT CHANCE OF
THUNDERSTORMS WILL CONTINUE TO EXIST. THE DRIER AIR WILL ALLOW TEMPS
TO WARM BY SUN AND INTO THE FIRST PART OF NEXT WEEK. BY TUES ANOTHER
TROF WILL BE APPROACHING THE PACIFIC NW COAST FORCING THE UPPER HIGH
TO RELOCATE ITSELF IN THE 4 CORNERS REGION. THIS WILL RETURN A SE
FLOW TO SOUTH CENTRAL AZ AND A GRADUAL RETURN OF MOISTURE FOR A
SLIGHT CHANCE OF THUNDERSTORMS SPREADING WEST INTO THE SOUTH CENTRAL
AZ BY MID WEEK. WITH THE RETURN OF MOISTURE... TEMPS ACROSS SOUTH
CENTRAL AZ WILL SLOWLY BEGIN TO LOWER BY MID WEEK. A SW FLOW WILL
KEEP SW AZ SE CA DRY THRU MID WEEK.

&&

.AVIATION...
00Z TAFS ADEQUATELY DEPICT EXPECTED WEATHER. SEE TAFS
PHXTAFPHX...PHXTAFIWA...PHXTAFYUM...LAXTAFBLH AND LAXTAFIPL FOR MORE
DETAILED INFORMATION.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

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22/DKS